The hero is Daisaku Kusama who encounters an enormous robot "Giant Robo 1 (GR1)" at ruins in Okinawa. He makes a contract with an ancient to be the commander of GR1. Daisaku is genetically modified to become one with GR1 to fight. The ally organization is "UNISOM." The enemy organization is "Gigantic Rebellion Operators (GRO)." They manipulate Giant Robos and start "armored terrorism" through the world. The mysterious girl in this anime is V. V is a girl who appears in front of Daisaku like an illusion. Her relationship between the GR is unkown.